1. Field of the Invention
The present invention relates to a process for reducing gaseous pollutants in the air, namely nitrogen oxides (NOx), sulfur oxides and/or carbon monoxide (CO), which are produced by combustion of hydrocarbons or hydrogen in an engine or boiler, and primarily, in a gas turbine. The present invention is also directed to an apparatus for performing the process and a process for making the reactor/catalyst absorber.
2. Art Background
Turbine power plants are becoming the standard for generating electricity because they are so efficient compared to any other form of power manufacture. Turbine power plants that burn methane to produce power for residents and manufacturing facilities in cities also produce carbon monoxide and nitrogen oxide as pollutants. It is highly desirable to reduce or eliminate these pollutants so that the air is not contaminated as a result of power production.
Initially, the permitted level of pollution by power plants for nitrogen oxides (NOx), which includes nitric oxide (NO) and nitrogen dioxide (NO.sub.2), was less than 100 parts-per-million (ppm) and the level of carbon monoxide (CO) was to a level of less than 100 ppm. Later, a second step was taken to reduce the NOx to less than 25 ppm and the CO today is still permitted at any amount less than 100 ppm. Using current technology, the output levels of NOx can be reduced to the range of 5 to 9 ppm plus NH.sub.3 slippage resulting from the selective catalytic reduction (SCR) technology described below.
The only technology which is currently available to obtain the 5-9 ppm NOx levels is called selective catalytic reduction, in which ammonia is mixed with flue gas and then passed over a catalyst which selectively combines the nitrogen oxides and ammonia to eliminate a major portion of the NOx. One problem with the selective catalytic reduction is that as a practical matter, it is only capable of reducing the NOx to the range of 5 to 9 ppm. Another problem referred to as slippage, is caused by hazardous ammonia passing through the catalyst.
Another problem of the SCR technology is that the operating conditions required for SCR are only achieved by expensive modifications of the down stream boiler or heat exchanger system.
There have been other technologies for reduction of pollution which have been advanced, such as overwatering in the combustor, and these also have the potential to reduce the NOx pollution, but none of them reduce the NOx to levels much less than 5 to 9 ppm.
In a copending application owned by the assignee of the present application, a system comprising essentially a two step process has been described. In the first step, the stack gases are first contacted with a catalyst under certain conditions which cause the oxidation of certain oxide pollutants, including NO and CO. In the second step, the oxidized pollutants are absorbed in an absorption bed.
It would be desirable to combine the oxidation and absorption steps into a single step performed by a single material.